1. Field of Invention
The present invention relates generally to 90% Annual Fuel Utilization Efficiency (AFUE) gas furnaces and water heaters. 90% AFUE devices bring combustible air into the device from outside the structure being heated through an outside air conduit with a screen cap on the outside end. When outside temperatures drop below 10 degrees Fahrenheit, the inlet air screens tend to freeze or get covered in snow. More particularly it discloses an alternate intake apparatus that is installed on the outside air conduit that opens automatically to a second source of combustible air inside the heated structure when the inlet air screen from outside is blocked or frozen.
2. Prior Art
90% AFUE gas furnaces have a combustible air inlet conduit that runs from outside the building to the combustion chamber of the furnace or water heater. Typically they have a screen cap over the inlet end to prevent entrance of pests into the conduit. The inlet screen of this conduit tends to freeze-up or become blocked with snow and ice when the outside temperature falls below 10 degrees Fahrenheit. Prior art attempts to resolve this problem include numerous expensive service calls to knock the ice off the conduit screen or even worse, calls to repair extensive damage from frozen water lines in an unattended home. To date the prior art attempts to resolve this problem have been ineffective and costly.